The selective extraction of organic solutes from organic solvents by water on the basis of relative partitioning of the organic solute between organic and aqueous phases is known, but, as a practical matter, has been restricted to organics that exhibit high coefficients of partition in water. The principal reason for this is that the selective aqueous extraction of organics with low partition coefficients would require impractically large volumes of water, which in turn would require large energy input to evaporate the water so as to isolate the extracted organic component.
European Patent Application No. 0 329 347 discloses the extraction of cholesterol from melted butter or oil with a methanol/water mixture containing 1-2 wt % water. Following extraction, the methanol/water mixture was cooled, then distilled to provide resuable methanol/water extractant. In addition to solvent recovery by distillation, the same Application discloses solvent recovery by passage through a loose RO membrane. However, there is no disclosure or suggestion of coupling the solvent recovery step with the extraction step nor of any efficiencies which might be realized from such a coupling.
The present invention overcomes the inherent limitations of aqueous extraction of organics, allowing selective extraction of organic solutes with low coefficients of partition in water, providing a means of trapping or concentrating such low-partitioning organic solutes, and allowing recycling of extractant.